Cathode support



1949- c. v. LITTON CATHODE SUPPORT Filed Nov. 1, 1945 II'IIIIIIIH QN .w A A, w EN n.. h

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Patented `une 28, 1949 CATHODE SUPPORT Charles V. Litton, Redwood City, Calif., assignor to Federal Telephone and Radio Corporation, New York, N. Y., a corporation of Delaware Application November 1, 1945, Serial No. 62.6,132

(Cl. Z50-27.5)

8 Claims.

This invention relates to vacuum tubes and in particular to a supporting means for iilamentary cathodes. More specifically the invention provides an improved mechanical structure of great rigidity for supporting a filament of the binlar type. Although the supporting structure may in general be employed with vacuum tubes of all types, it is particularly useful with magnetrons of the plural cavity type and therefore the preferred embodiment of my invention will be illustrated and described in connection With a tube of this type.

In addition to the improved mechanical features of my cathode support structure, there are also many advantages of an electrical nature, especially when employed with very high frequency generators such as magnetrons. For example, my improved support provides for substantially complete shielding against stray electron emission from the filament which otherwise tends to cause the magnetron to oscillate at undesired frequencies or modes. Means are also provided whereby the cathode may be made to assume substantially a radio frequency ground potential during operation.

It is therefore one of the objects of my invention to provide an improved type filament support possessing great rigidity and freedom from vibration.

Another object of my invention is to provide a rigid filament support that is particularly adapted for use with magnetrons of the plural cavity resonator type.

A further object is to provide a filament support that prevents stray electron emission from electing the operation of the vacuum tube with which it is associated.

A further object is to provide a support for a filament that assumes substantially a radio frequency ground potential when in operation.

Additional objects and features of my invention will be apparent from the following description and the appended claims.

As above noted my invention Will be described as it is embodied in the construction of a plural cavity magnetron and as illustrated in the attached drawings of which:

Fig. l is a cross sectional View of a plural cavity magnetron, the section being taken through what is essentially the axis of symmetry of the cathode and supporting structure therefor.

Fig. 2 is an enlarged section of the filament and its supporting structure showing more clearly and in greater detail the features of its construction. l.

Referring first to Fig. l, reference character l represents the body of the magnetron to which other parts are brazed or otherwise suitably fastened until a stucture capable of being evacuated has been formed. On one side of the body is a cylindrical extension 2 While on the other side there is a similar but shorter cylindrical extension 3, both extensions being brazed to the body l.

The extension or housing 2 encloses an assem bly l for adjusting the frequency to which the magnetron may be tuned as will be hereinafter described. This adjusting mechanism does not constitute a part of my present invention and a detailed description will therefore not be given. However in general, a platform 5 is brazed to a Sylphon bellows which is in turn bra/eed to a bearing holder l, the latter being brazed to housing 2 along the circumference 8. When the magnetron is evacuated, the external atmospheric pressure tends to extend the bellows and force the platform 5 inwardly. This tendency must be constrained and a method for accomplishing same will now be described. A rod 9 is also brazed to the platform 5 and extends through the bellows and the bearing holder. A hardened and ground sleeve l0 is held in position over the rod by the tongue nut Il and the lock nut l2. The tongues I3 lt into slots in the sleeve lil. When the nuts are tightened this prevents any relative motion between the rod and the sleeve.

A bearing I4 is positioned over the sleeve l0 and is clamped against the bottom of the bearing holder l by the inner ball race l5. The thrust bearing ball retainer with balls It and the outer ball race Il are held against the race l5 by the atmospheric pressure and the nut I8, the latter bearing against the race Il. Relative rotation between the nut I8 and the sleeve lll determines the extent of the longitudinal motion of the platform 5. A control knob I9 is fastened tothe nut I3 for turning the latter. A scale 20 is located on the outer diameter of the knob and is aligned adjacent a xed scale 2| on the indicator ring 22, the latter being clamped to the extension 2 as shown. A measure of the longitudinal motion is thus obtained.

On the aforementioned cylindrical extension 3 is mounted the cathode support assembly of my invention. A support cup 23 is brazed to the extension 3 and to a tubular sealing member 24. This member and the other members which are part of the metal to glass seals for insulating the cathode supporting members one from another. is preferably made of a metal having approximately the same thermal expansion ras hard glass.

3 up to about 465 centigrade such as commercial alloys of iron, nickel and cobalt or other suitable material. Sealed to the member 2t is an insulating portion 25 followed by a series of three metal cups 2B, 21, and 28 separated by glass portions 29 and 30.

To the metal cups are attached the two supporting members 3| and 32 for the cathode 33. Both supporting members maybe frustrurns of cones as shown or they may be other conoidal shaped bodies. The dimensions of the conical frustrums at the apical ends (point 34) are such that, were the cones annular at this point/they would intersect to form a common circle. -However, the frustrums are so mutilated that each of them at the point 34 are arcuate or semi-annular. In other words, if a planeperpendicular to the common axis of the frustrums, were passed through the point 34, the section would show two semi-circular arcs about a common center. The frustrums are cut away or mutilated from their apical endsftoward their bases a distance suilioient to permit the central support 35 to pass freely therethrough7 i. e., without making electrical contact with the frustrums.

.From the point 34 to the ends of the members 3l and 32 their shape is substantially semicylindrical. These semi-cylindrical portions are welded or otherwise fastened to semi-cylindrical members 36 and 31. To the other ends of these semi-cylindrical members is attached the biflar filamentary cathode 33, one end of one filament being connected to one member and one end of the otherlament being connected to the other member. The opposite ends of the filaments are attached to a member 38. This member maybe grooved as shown to improve its heat radiating properties. It will be noticed that the cathode extends into a recessed portion of the member 38 for -the purpose of shielding the active region of the magnetron from undesired electron emission from that portion of the cathode within the recess. Similarly, there is connected to one of the semi-cylindrical members 31 a cylindrical ring memberlSQ. This last named member also serves to shield the active region of the magnetron from undesired emission from the filament. It is well-known that the ends of a filament are usually coolerthan the central portion thereof due to heat being conducted to the lament supports. By shielding the ends of the lament as described above, that portion of the filament between the ends of the shields emits electrons substantially uniformly.

Connected to the Kovar cup 28 is a central support 35. From the end of the support nearer the cathode, a smaller rod 40 extends through the semi-cylindrical members, 36 and 31, the -bifllar windings of the cathode, and the support 38, it being welded or otherwise fastened to the latter. For greater rigidity and freedom from possible vibration the rod 40 may be extended into a bearing in an insulating support ring 4I, the latter being held in place within the pole piece 42 by welding a ring 43 to the pole piece as shown. It is preferable that the effective length of the rod 40 together with the cathode 33, from a point adjacent the center of the cathode to the free end of the rod, be substantially a quarter wave length long, or an odd multiple thereof, at the mean operating frequency of the magnetron. This will cause a potential mode to exist at the center of the cathode and provide a symmetry of operating potentials conducive to improved operation of the magnetron. v

fsired `mode.

Athe frequency of oscillation is dependent upon the dimensions of the structure it becomes difficult to always force oscillations to occur at the de- To `shield other parts of the magnetron from electrons which may tend to pass through the slot '44, a, circular shield l5 is fastened tothe member 39 Vaslshown in detail on Fig. 2 of the drawing.

Themagnetron is evacuated through holes 46 in the central supportI member 35 and when the vacuum-has-.been drawn the magnetron is sealed oT-attheitips.

As above described .thecathode comprises two fllamentary windings so mounted and energized as to constitute abilarxfilament. The windings are preferably 0f thoriated tungsten. n a bifilar filament the current inffadjacent turns flows `in opposite directionsrwith the .result that-.the magnetic eld due to the current .is substantially neutralized. If v`alternating -current is employed J@3o-energize the cathode, as is .usually the case in practice, the small amount of residual alternating' ux -is insuicient .to appreciably modulate the magnetronroutputcurrent. Power for ener gizing-the cathode v-may-beiapplied by connecting thepower supply leadsfto-the Lterminals Brand 133, these terminals being .screwed onto threaded rings 5E and-5i respectively. lIhe rings are brazed to the metal lcups 23 and 21 thus insuring good electrical connections-throughout. If it is. desired that a, connectionbemade tothe electrical center of the cathode this connection may be made to the ring-52, which is screwed to the threaded ring 33, the latter-being welded to the metal cup k28.

In the magnetron of my invention a 4tuning structure is also provided which `is 4the subject matter of anotherlotmyinventions'described and claimed Yin my copending yapplication Serial No. 626,130, entitle-d Adjustable magnetron, and filed November 4il, 1945.

Many modifications of my invention will occur to one skilled inthe -art and vit is vrmy intention that my invention be not Ylimited -to Athe single embodiment shown but only bythe scope of lthe appended claims:

What is claimed is:

l. Supporting means for a cathode for an electron ldischarge device comprising a `rst conoidal body mutilated at the apex to provide an essentially semicircular end vandhaving an annular base end, a second conidal body arranged coaxally with said'rst conidal body and also mutilated at the apex ,to provide a similar essentially semicircular end and forming with said first mentioned arcuate end a circle, said second conoidal body having an annular' base end, and mounting means comprising separate conducting portions and an insulating portion therebetween, said conducting Iportions .each mounting a base end.

.2. Supporting means .in accordance with claim 1 wherein `the annular base 4end .of yone conoidal body is smaller ,than the base end of .the other body and wherein the conducting portions of said conoidal body having an annular base end, supporting means comprising separate conducting portions and an insulating portion therebetween, said conducting portions each mounting a base end, said conoidal bodies being spaced one from the other, and means connecting said filament to said semicircular ends.

4. A cathode as claimed in claim 3 in which said filament comprises a bifilar filamentary winding.

5. A cathode as claimed in claim 3 in which said lament comprises a bifilar lamentary winding and said means connecting the cathode to the semicircular ends comprises a pair of substantially semi-cylindrical members, each member being connected to one terminal of said winding and to one semicircular end.

6. A cathode as claimed in claim 3 in which said filament comprises a bilar filamentary winding and which further comprises a center support for said lament, means connecting one end of said center support to the center of said winding, and means arranged on the other end of said support for directly connecting said support to said envelope.

7. A vacuum tube for operation over a predetermined range of frequencies comprising an envelope, a cathode filament inside said envelope, a rst conoidal body mutilated at the apex to provide an essentially semicircular end and having an annular base end, a second conoidal body arranged coaxially with said first conoidal body and also mutilated at the apex to provide a similar essentially semicircular end and forming with said iirst mentioned semicircular end a circle, said second conoidal body having an annular base end, said supporting means forming part of said envelope and mounting said conoidal bodies inside said envelope and spaced one from the other, means connecting the ends of said lament to said semicircular ends, and a central supporting rod having one end connected to said envelope and the other end connected to the center of said Winding, said rod extending beyond said filament cone nectiori a distance substantially equal to a quarter wave length of the operating frequency of said tube, whereby said cathode is maintained at substantially radio frequency ground potential.

8. A vacuum tube according to claim 7 further comprising shielding means surrounding both said semicircular ends and said means connecting said filament to said ends and a connection between said shielding means and one only of said semicircular ends for conning the emission from said lament.

CHARLES V. LITTON.

REFERENCES CITED The following referenlces are of record in the le of this patent:

UNTED SIATES PATENTS Number Name Date 1,797,990 Lucian Mar. 24, 1931 2,169,396 Samuel i Aug. 15, 1939 2,406,276 White Aug. 20, 1946 

